This invention relates to an enzyme activated process for coloring hair.
Pre-formed dyes for coloring hair have not gained wide acceptance due to their general failure to impart colors to hair which are sufficiently imitative of natural hair colors. Products which contain reactants such as H.sub.2 O.sub.2 and an oxidation dye precursor (i.e., a precursor which forms dyes in situ on the hair through an oxidative process) do produce colors which are closely imitative of natural hair color and have obtained reasonable commercial success. These latter products, however, because of the severe oxidizing conditions required (i.e., performing the oxidation at H.sub.2 O.sub.2 concentration of 3% or more and a pH of 8.5 or higher for time periods in excess of 20 minutes) and the high concentrations of oxidation dye precursors needed to produce the desired coloration can cause skin irritation and sensitizatin as well as hair damage to some users. Further, the ammonium hydroxide which is generally used to maintain the high pH in these products has an odor which is offensive to most users.
U.S. Pat. No. 3,251,742, issued May 17, 1966, teaches an enzyme based oxidative process for dyeing hair at substantially neutral pH, wherein oxygen from the atmosphere is the oxidizing agent. The enzyme is an oxidase (e.g., tyrosinase or laccase) and the dye precursor is a combination of an aromatic polyhydric compound and an aromatic amine. Surprisingly, it has been found, according to the process of the present invention, that an oxidative coloring process based on hydrogen peroxide and soybean peroxidase enzyme can be carried out under mild oxidizing conditions and does not require a dual oxidation dye precursor system comprising an aromatic polyhydric compound and an aromatic amine. Either type of compound can be used alone as the oxidation dye precursor in the present invention. This provides more flexibility in selection of the oxidation dye precursors and thus more freedom in the choice of colors to be produced.